Abstract

The design, fabrication, and characterization of an integrated 2D photonic crystal stack are described for application as optical filters with improved optical density and angle tolerance compared to single photonic crystal slabs. The 2D photonic crystals are designed as polarization independent reflectance filters with a narrow spectral bandwidth centered at λ = 532 nm by utilizing the guided mode resonance effect. Up to three photonic crystal layers are vertically stacked upon a single plastic substrate by using repeated nanoreplica molding process steps, with no alignment required between stacked layers. The photonic crystal stack filters achieve optical density of 2.24 with an angular tolerance of 14.8 degrees.

Figures (10)

(a) SEM view of the nanoreplica mold from a 2D square lattice photonic crystal silicon master. The master is comprised of posts resulting in a nanoreplica mold of 2D square lattice of holes. (b) AFM section view of nanorpelica mold showing a period of 300 nm and hole depth of approximately 150 nm.

(a) Cross section schematic view of a 3 PC stack filter with 300nm period, hole depth of 150 nm, and TiO2 thickness of 67 nm. A single filter would consist of layers 1, 2, and 3 in the schematic. The schematic cross section is not to scale, as the UVCP layers (layers 1, 3, and 5) are each ~5 μm thick, and the PET substrate is ~250 μm thick . (b) Top view of the 2D PC filter with corresponding directions of the Brillouin zone with respect to the lattice vectors.

Schematic of the in situ reflection spectrum monitoring system. The low vacuum environment is inside the dashed box. In one leg of the bifurcated optical fiber, incident light is illuminated onto the device through a collimator and lens optical system. The reflected light is collected through the same optics and sent to the other leg of the optical fiber, where it is measured with a spectrometer.

Setup used to acquire the transmission spectrum of the PC stack filter during different stages of the fabrication process. Broadband light from a tungsten halogen lamp is incident on the device and the transmitted light is collected and analyzed using a spectrometer.

Band diagram of the 2D PC filter in the Г-Χ (plots a & b) and Г-Μ (plots c & d) directions. Color scale represents 0% transmission (blue) to 100% transmission (red). The Г-Χ band diagram has a flat band effect that is clearly not seen in the Г-Μ direction. The reference device (plots b & d) has smaller angular FWHM than the stack PC filter (plots a & c) due to its smaller resonance line width that is seen in the band diagram.

Comparison between theory and experimental data for increase in OD as a function of number of PC filters in a stack. The experimental results are lower than the predicted values and show a diminishing increase in OD with additional PC filters incorporated into the stack.